This invention relates to tilt limit detecting apparatus in general and more particularly to an improved tilt limit detector which is capable of withstanding higher degrees of shock and vibration.
A tilt limit detecting apparatus is disclosed in U.S. Pat. No. 3,813,556 in which a bubble level contains a prescribed amount of opaque fluid and a photo detector arrangement transverse to the longitudinal axis is provided to sense bubble movement in response to tilting of the device. The photo detector arrangement includes a pair of light source-photo cells combinations, the first of which is normally positioned at the center of the bubble in the level position with the second combination spaced the distance y from the first such that the distance y is less than the bubble length x. The opaque fluid acts as a shutter interposed between the light source-photocell combinations so that with the connection of suitable electronic circuitry to the photocells angular tilts in excess of the allowable limit which generally equals x/2 in radians are detected as well as the particular direction, clockwise or counterclockwise identified.
Although this device works well in some applications it suffers from a number of deficiencies. Since its principle of operation is based on bubble size i.e., the bubble length must be larger than the light source-photocell combination spacing, it is unsuitable for a switch with a great length of bubble travel, large tilt switching angles and consequently for a switch to endure environmental adversities. During shock and vibration the deformation of the bubble and its switching travel length are closely related. Thus, the switch disclosed in the aforementioned patent is not recommended for dynamically affected vehicles, platforms or devices. The described switch was designed primarily for a static condition.
In view of these deficiencies of the prior art device the need for an improved tilt limit detecting apparatus of this nature which is capable of operating with great lengths of bubble travel and is not susceptible to shock and vibration becomes evident.